This invention relates to methods for the preparation of 4-hydroxy-and 4-trimethylsiloxy-benzocyclobutene.
Benzocyclobutene (BCB)-based polymeric materials have recently attracted growing attention and research interest in the area of structural and electronic applications because of the versatile chemistry of benzocyclobutene as well as the combined advantages of processability and properties. The cure chemistry of benzocyclobutene is based upon the propensity of the four-membered ring to undergo electrocyclic ring-opening at elevated temperatures (.about.200.degree. C.) to provide reactive o-quinodimethane that will undergo dimerization and polymerization, or react with an attendant dienophile to form a Dieis-Alder adduct. ##STR1##
Research reports describing the synthesis and characterization of high-temperature BCB-based materials for potential structural and aerospace applications have appeared. These heat-resistant thermosets include, for example, homopolymerized bisbenzocyclobutene-terminated imide monomers and a variety of resins generated from Dieis-Alder reactions of bisbenzocyclobutene-terminated imide monomers with monomers containing dienophilic end-groups such as acetylene, phenylacetylene and maleimide. Recently, the incorporation of the thermally reactive benzocyclobutene into the main chain of polymeric materials for lateral crosslinking has also been reported. The objective was to improve the compressive strength of high modulus fibers such as Kevlar.RTM. via the use of a latently crosslinkable monomer, 1,2-dihydrocyclobutabenzene 3,6-dicarboxylic acid.
4-Aminobenzocyclobutene (4-AMBCB) is a simple, polymerizable endcapping agent that has been used for the preparation of bis(benzocyclobutene) (BBCB)-terminated monomers for heat-resistant, thermosetting polyimides. Another simple BCB-endcapping agent bearing a nucleophilic center is 4-hydroxybenzocyclobutene (4-HOBCB). As its molecular structure suggests, 4-HOBCB can be used in the performance enhancement of a number of important engineering thermoplastics, such as polyethersulfones (PES), polyetherketones (PEK), polycarbonates (PC), whose syntheses require phenolic starting materials. For example, the network polymers derived from bisphenol-A polycarbonate terminated with 4-HOBCB have shown excellent solvent and ignition resistance, as well as good toughness over a broad range of crosslink densities. It has also been shown that systems derived from AB-benzocyclobutene (BCB)-maleimide (MI) monomers were easy to process and the resulting matrix maerials were much tougher than other advanced thermosets for aerospace applications. 4-HOBCB was an important ingredient for a number of these AB-BCB-MI monomers. Another important advantage of 4-HOBCB over 4-AMBCB is its amenability to a large-scale, environmentally benign synthesis process using a biocatalyst in an aqueous medium.
4-HOBCB was first prepared from bis(4-aminobenzocyclobutene) sulfate under diazotization conditions. It can also be synthesized from benzocyclobutene-4carboxaldehyde via a modified Baeyer-Villiger reaction using permonophosphoric acid prepared from 70% hydrogen peroxide solution and phosphorus pentoxide, or from copper-catalyzed nucleophilic substitution reaction of an alkali hydroxide and 4bromobenzocyclobutene. Additionally, it has been demonstrated that benzocyclobutene can be enzymatically dioxygenated to an intermediate diol which undergoes facile dehydration to 4-HOBCB.
We have discovered a novel method for the preparation of 4-HOBCB. We have also prepared a new substituted benzocyclobutene compound.
It is therefore an object of the present invention to provide a novel method for the preparation of 4-HOBCB.
It is a further object of the present invention to provide a new substituted benzocyclobutene compound.
Other objects and advantages of the present invention will be apparent to those skilled in the art.